Wilderlands Age of Worms
The brains behind the gang of doppelgangers inhabiting the Sodden Hold, Telakin appeared first disguised as Master Penkawr, then changed into an orc barbarian. The party defeated him rather quickly and discovered that he was, in fact, another doppelganger, albeit a kind of special one since he was able to use the special abilities of his alternate forms. After he shifted back to his true form, the party discovered that he had a curious tattoo on his forehead (see below). This, in combination with the missive written with a strange alien hand, leads the party to conclude that he and his band have been getting their orders from someone else. Pursuit of this someone else (Zyrxog) will lead several of them to their doom.
For a “greater” doppelganger, Telakin wasn’t so great.